In an optical communication network a main path is used for transmitting communications between two or more nodes. A typical such network also uses a protection path for use in a case where communication cannot be transmitted along the main path, e.g. a cut in the optical fiber, etc. There are many risk factors that may render such a main path inoperative, such as an earthquake, an explosion, and careless human operations such as cutting a fiber during digging in the vicinity of the fiber. Therefore, careful selection of a pair of main and protection paths is required, in order to minimize the risk that both paths become inoperative as a consequence of a single damaging effect. This pair of paths, main and protection, is known as a protected trail.
In order to provide a tool for enabling a network operator to select a suitable pair of such main and backup paths that provides acceptable diversity, a concept of grouping segments of the network into Shared Risk Link Groups (SRLGs) has been suggested in order to allow the selection of main and protection paths by not allowing any SRLG to be common to both paths. This concept is described in an excerpt from an Internet Engineering Task Force (IETF) draft document, work in progress, draft-ietf-ipo-impairments-00.txt, by Chiu et al, May 2001, the disclosure of which is hereby incorporated herein by reference.
However, when trying to implement the concept described in this reference, in order to obtain a diversified pair of main and protection paths that conform with the reliability requirements of the operator, the operator must input many parameters such that only when taken together guarantee the required relationship between any such two selected paths. For example, in order to avoid disruptions in the optical communication network at a certain degree of confidence, the network operator may want to avoid the main and protection paths to have any number of the following: a common duct; a common conduit; and common central office (CO) equipment. Bearing in mind that many protected trails need to be provisioned, it is understandable that this task imposed on the operator is a rather complicated task. Therefore, simpler mechanisms that will allow the selection of suitable pairs of main and protection paths are desired.